B-H curve in different frequency

hi

i have question about B-H curve for magnetic liberary cores.

when we change frequency the B-H curve should change, but it doesn't! why?

my circuit is :

B-H curve for 25 KHz:

B-H curve for 50 Hz:

core loss is equal!!

i've changed frequency , 50 Hz, 25 KHz, 50 KHz.